Far-Out Theory Ties SARS Origins to Comet

Stefan Lovgrenfor National Geographic News

June 3, 2003

The source of SARS has mystified medical experts. Some believe it evolved naturally in humans. Others say it must have jumped from an animal, maybe a chicken or an exotic bird. But one group of British scientists suggests a more far-out origin: space.

In a letter to the British medical journal The Lancet, Chandra Wickramasinghe, from Cardiff University in Wales, and other scientists, propose that SARS may have originated in outer space then fallen down to Earth and landed in China, where the outbreak began.

It sounds like a headline from a supermarket tabloid, but the idea may not be as outlandish as it first appears. One hundred tons (90 metric tons) of space debris fall on Earth every day; some scientists believe as much as one ton (0.9 metric ton) of bacteria from space is part of that daily deposit.

Particles carrying the SARS virus could have come from a comet, the researchers say, and released into the debris trail of the comet's tail. The Earth's passage through the stream would have led to the entry of the culprit particles.

"We're not saying this is definitely what happened," said Wickramasinghe, who is also the director of the Cardiff Centre for Astrobiology, a research effort that seeks evidence of extraterrestrial life. "But the theory should not be ruled out."

SARS, or severe acute respiratory syndrome, has so far infected at least 8,384 people and claimed 770 lives. Mainland China, Hong Kong, Taiwan, and Canada have been hit hardest by the epidemic.

Independent Evolution

Although SARS has been identified as a coronavirus, the virus is unexpectedly novel. An independent evolution of the virus may have been required, which, Wickramasinghe says, adds credibility to his argument that SARS has an external origin.

According to his theory, a small amount of the virus introduced into the stratosphere could have lead to an initial fallout east of the Himalayas, where the stratosphere is thinnest, followed by sporadic deposits in neighboring areas.

"There would be a first point of descent," said Wickramasinghe. "This could have been in China."

But most medical experts are sticking to a more conventional explanation for the origin of SARS.

"We have no scientific evidence that SARS or any other infectious disease has dropped off a meteor at this point in time," Julie Gerberding, director of the Atlanta-based Centers for Disease Control and Prevention, said at a recent briefing. "Should we discover any evidence supportive of that, we would let you know.

Gerberding said SARS is most explainable by natural evolution of coronaviruses, either from an animal or a poultry source, or possibly a coronavirus that's evolved in a human. "We have many hypotheses that are far more plausible than meteorites," she said.

Collecting Bacteria

About 100 tons (90 metric tons) of comet debris reach the Earth on a daily basis, and Wickramasinghe says there is evidence for life arriving with this debris.

In an experiment two years ago, he and scientists from the Bangalore-based Indian Space Research Organization sent sterile collecting devices into space and brought back large quantities of microorganisms in samples of stratospheric air captured at an altitude of 26 miles (41 kilometers). The researchers were able to culture, or grow, two types of microorganisms, which proved similar to known terrestrial species.

"Our findings lend support to the view that microbial material falling from space is, in a Darwinian sense, highly evolved, with an evolutionary history closely related to life that exists on Earth," said Wickramasinghe.

He estimates that a ton (0.9 metric ton) of bacterial material falls onto Earth every day, translating into more than 1,000 types of bacteria. Most of this material simply adds to the unculturable or uncultured microbial flora present on Earth.

The researchers argue that the random nature of epidemics adds credence to their argument that disease-causing bacteria and viruses may be evolving in outer space, parallel to those on Earth.

"New epidemics have a record of abrupt entrances from time to time," said Wickramasinghe. "The patterns of spread of these diseases are difficult to explain simply on the basic of endemic infective agents."

He says the unusual nature of major epidemics, such as the influenza epidemic of 1917-19, where infection rates were not easily explained by epidemiological modeling, bears the hallmarks of a space incident.

"Although person-to-person spread occurred in local areas, the disease appeared on the same day in widely separated parts of the world on the one hand, but, on the other, took days to weeks to spread relatively short distances," said Wickramasinghe.

The Origins of Life on Earth

The idea that SARS may have originated from space is based on the argument that life first appeared on Earth some four billion years ago when the Earth suffered a prolonged period of comet impacts.

This is a controversial theory. Most scientists believe that life on Earth began as a "primordial soup" in a lake or pond some 3.5 billion years ago: Chemicals from the atmosphere combined with some form of energy necessary to make amino acids (the building blocks of proteins) to create the first primitive organisms, kicking off the evolution of all species on Earth.

Wickramasinghe disagrees. He believes life did not start on Earth, but evolved on a much bigger scale, in a cluster of galaxies. Earth merely became an "assembly station" for all the cosmic genes.

"If Earth evolved in a closed-box situation, the argument we're making about SARS would not carry much weight," he said. "But if you accept the argument that life on Earth started from the outside, then all viruses originated from the outside."